U.S. patent application number 12/090959 was filed with the patent office on 2008-12-18 for short-distance wireless data transmitting apparatus and method.
This patent application is currently assigned to OPEN SOLUTION CO., LTD.. Invention is credited to Suk-whan Choi, Keun-ho Jang, Young-hee Lim.
Application Number | 20080310379 12/090959 |
Document ID | / |
Family ID | 37962641 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080310379 |
Kind Code |
A1 |
Lim; Young-hee ; et
al. |
December 18, 2008 |
Short-Distance Wireless Data Transmitting Apparatus and Method
Abstract
A short distance wireless data transmission system and method
which are capable of minimizing data loss are disclosed. The short
distance wireless data transmission system can monitor variation
amount of memory data, which is buffered in the master side when
data transmission errors occur, can perform re-transmission of data
having transmission errors, and can perform a change toward new
replacement channel without interference if variation amount of
memory data, which is buffered therein, exceeds a predetermined
reference value to re-transmit from data in which the first
transmission error occurs thereto, such that real time data cannot
be lost, although a channel change is generated by successive
channel interference.
Inventors: |
Lim; Young-hee;
(Gyeonggi-do, KR) ; Jang; Keun-ho; (Seoul, KR)
; Choi; Suk-whan; (Gyeonggi-do, KR) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
OPEN SOLUTION CO., LTD.
Seoul
KR
|
Family ID: |
37962641 |
Appl. No.: |
12/090959 |
Filed: |
October 20, 2005 |
PCT Filed: |
October 20, 2005 |
PCT NO: |
PCT/KR2005/003502 |
371 Date: |
August 8, 2008 |
Current U.S.
Class: |
370/338 |
Current CPC
Class: |
H04W 84/10 20130101;
H04W 28/14 20130101; H04W 36/06 20130101; H04W 24/00 20130101; H04L
1/18 20130101; H04W 36/02 20130101 |
Class at
Publication: |
370/338 |
International
Class: |
H04Q 7/24 20060101
H04Q007/24 |
Claims
1. A short distance wireless data transmission system, which
includes a transmission data generation unit for adding a
redundancy to data to be transmitted and then outputting the data,
and a received data processing unit for recovering data included in
received backward packet to original data, and then outputting the
original data, the system comprising: a memory controller for
storing inputted real time data in a memory, for reading real time
data necessary for packetization from the memory to output the
packet to the transmission data generation unit, for checking
variation amount of data stored in the memory every time a
re-transmission request of real time data in previous frame is
received through a backward packet such that the real time data of
the previous frame can be re-transmitted or a channel change is
requested; a transmission/reception controller for performing
forward packetization for real time data outputted from the
transmission data generation unit together with header information
to transmit the forward packet through a setting channel, such that
a channel without channel interference is searched for per a
replacement channel test period to store the searched channel as a
replacement channel, and present setting channel can be changed to
the replacement channel when a channel change of the memory
controller is requested; and an RF transmitting/receiving unit for
communicating the forward packet and backward packet with the slave
side in wireless interface fashion.
2. The system as set forth in claim 1, wherein the memory
controller provides record position information of real time data,
which is read from the memory, and output position information,
which is calculated from output position indication information
included in the backward packet, to the transmission/reception
controller, in which the record position information and the output
position information is a part of header information.
3. The system as set forth in claim 2, wherein the memory
controller re-transmits real time data transmitted in a previous
frame if record position information of real time data transmitted
in the previous frame is identical to subsequent record position
indication information within the backward packet, and requests
channel change if variation amount of memory data in retransmission
intervals of real time data exceeds a channel change reference
value.
4. The system as set forth in claim 1, wherein the
transmission/reception controller searches for the replacement
channel without channel interference such that accumulation average
of error bit of sync field in the backward packet, which is
received through the setting channel for a predetermined interval,
is compared with error bit of sync field of backward packet which
is received through the replacement channel in a replacement
channel test interval.
5. A short distance wireless data transmission system, which
includes a transmission data generation unit for adding a
redundancy to data to be transmitted and then outputting the data,
and a received data processing unit for recovering data included in
received backward packet to original data, and then outputting the
original data, the system comprising: a memory controller for
storing real time data, which is recovered in the receiving data
processing unit, in a memory address which is indicated by record
position information within a forward packet, for generating
subsequent record position indication information indicating the
memory address in which real time data of the subsequent forward
packet must be stored, and output position indication information
of real time data which is presently outputted from a memory, and
for outputting the information thereto; a transmission/reception
controller for variably setting a setting channel according to
control information within wireless received forward packet, for
performing backward packetization for subsequent record position
indication information and output position indication information,
which is inputted from the memory controller, together with
non-real time data, and for transmitting the packet thereto; and an
RF transmitting/receiving unit for communicating the forward packet
and backward packet with the master side in wireless interface
fashion.
6. The system as set forth in claim 5, wherein the memory
controller outputs real time data from the memory if the real time
data is stored in the memory address which is indicated by output
position information within the received forward packet.
7. A method for transmitting short distance wireless data,
comprising the steps of: storing real time data to be transmitted
in a memory; reading the real time data for packetization from the
memory to perform forward packetization of the real time data,
non-real time data, and header information, and transmitting the
forward packet to a slave side through the setting cannel; checking
as to whether there is a data re-transmission request in a backward
packet which is transmitted from the slave side through the setting
channel; comparing variation amount of data, which is stored in the
memory, with a predetermined channel change reference value, if the
data re-transmission request exists; after real time data in a
previous frame, which receives a re-retransmission request, is read
from the memory based on the comparison result, performing
re-transmission to the slave side or requesting a change toward a
replacement channel without interference to the slave side, in
which the replacement channel is searched for over a replacement
channel test interval; and performing transmission/reception of the
forward packet and backward packet through the replacement
channel.
8. The method as set forth in claim 7, wherein the forward packet
includes: a sync field in which sync information is recorded; a
control information field in which communication channel indication
information is recorded; a header field in which record position
information for indicating record position of real time data and
output position information for indicating data output position on
a memory is recorded; and a field in which non-real time data and
real time data are recorded, respectively.
9. The method as set forth in claim 7, wherein the backward packet
includes: a sync field in which sync information is recorded; a
control information field in which a response message is recorded a
header field in which subsequent record position indication
information, which indicates a memory address in which real time
data is recorded, and output position indication information of
real time data which is presently outputted from a memory; and a
field in which non-real time data are recorded.
10. The method as set forth in claim 7, wherein the replacement
channel is set to a replacement channel for testing, when an
accumulation average of error bit of sync field in the backward
packet, which is received through the setting channel for a
predetermined interval, is greater than error bit of sync field of
the backward packet, which is received through the replacement
channel for testing, which is temporarily set in a replacement
channel test interval.
11. The method as set forth in claim 7, wherein the replacement
channel for testing, which is temporarily set in the replacement
channel test interval, is set to one of frequency channels, which
is spaced apart from the present setting channel frequency by a
predetermined distance.
12. A method for transmitting short distance wireless data,
comprising the steps of: storing real time data in a forward
packet, which is received through a setting channel, in a memory
address which is indicated by record position information which is
transmitted together with the real data; performing backward
packetization for non-real time data, record position indication
information including record position in which real time data must
be stored in a subsequent forward packet, and output position
indication information of real time data which is presently
outputted from the memory, and then transmitting the packet to a
master side; and transmitting the backward packet while a
communication channel is varied according to control information in
a received forward packet.
13. The method as set forth in claim 12, further comprising the
step of: reading and outputting real time data from the memory if
the real time data is stored in the memory address which is
indicated by output position information within the forward
packet.
14. The system as set forth in claim 3, wherein the
transmission/reception controller searches for the replacement
channel without channel interference such that accumulation average
of error bit of sync field in the backward packet, which is
received through the setting channel for a predetermined interval,
is compared with error bit of sync field of backward packet which
is received through the replacement channel in a replacement
channel test interval.
Description
TECHNICAL FIELD
[0001] The present invention relates to a short distance wireless
data transmission system, and more particularly to a short distance
wireless data transmission system and method which are capable of
minimizing data loss.
BACKGROUND ART
[0002] A Bluetooth using a 2.4 GHz industrial scientific medical
(ISM) frequency band and a wireless local area network (LAN)
employs a spectrum spread method whose types are a frequency
hopping spread spectrum (FHSS) and a direct sequence spread
spectrum (DSSS).
[0003] The DSSS is a method to obtain spread signals as spread
codes that are multiplied by data, and the FHSS (, or a frequency
hoping method) is a method to obtain spread signals as frequency
bands that are transited according to spread codes. Especially, the
frequency hopping method performs a frequency hop for a carrier
frequency of signals to be spread at a predetermined time interval
according to hopping patterns and transmits the signals thereto.
Namely, the frequency hopping method serves to convert narrow band
signals to wide band signals with respect to time average. The
frequency hopping method has advantages in that a predetermined
hopping pattern is formed within an ISM band to comply with a
standard of each country, data can be transmitted through a
frequency suitable for the pattern to minimize frequency
duplication, rapid frequency conversion reduces losses by multiple
paths, and configuration can be simply implemented. Therefore,
presently, the frequency hopping method is adopted by low-price
wireless devices (for example, Bluetooth).
[0004] However, since the prior art frequency hopping method causes
a hopping regardless of interference source for the entire
frequency band, if a hopping is generated in a specific frequency
in which interference exists, packet loss may occur. Especially,
such a situation is serious in a case where data (voice, audio and
video) must be transmitted in real time. Namely, if errors in data
are not recovered, data quality is deteriorated.
[0005] In order to prevent such a problem, Bluetooth (Spec. ver.
1.2) takes a hopping method, such that it monitors a frequency, at
which a type of interference called an adaptive frequency hopping
(AFH) occurs, for a predetermined period to avoid the frequency.
Also, the Bluetooth adopts a method that, if errors occur in data
due to interference generated while data is transmitted in real
time, the data is retransmitted twice at most.
[0006] However, such a method to prevent the problem cannot prevent
data loss from successive channel interference. Because, although
the same data is retransmitted thereto twice, if errors by the
successive channel interference are generated, the current channel
must be changed to a new replacement channel. But, even if such a
channel replacement is performed, previously repeatedly transmitted
data has already been lost.
DISCLOSURE OF THE INVENTION
[0007] Therefore, the present invention has been made in view of
the above problems, and it is an object of the present invention to
provide to a short distance wireless data transmission system and
method which are capable of minimizing data loss which may be
caused by channel interference, without performing channel
hopping.
[0008] It is another object of the present invention to provide to
a short distance wireless data transmission system and method which
are capable of minimizing data loss which may be caused by
successive channel interference, and converting a current channel
to a replacement channel whose channel interference is relatively
low.
[0009] In accordance with an aspect of the present invention, the
above and other objects can be accomplished by the provision of a
short distance wireless data transmission system, which includes a
transmission data generation unit for adding a redundancy to data
to be transmitted and then outputting the data, and a received data
processing unit for recovering data included in received backward
packet to original data, as an error bit is searched for using the
redundancy included in the received backward packet, and then
outputting the original data, the system comprising: a memory
controller for storing inputted real time data in a memory, for
reading real time data necessary for packetization from the memory
to output the packet to the transmission data generation unit, for
checking variation amount of data stored in the memory every time a
re-transmission request of real time data in a previous frame is
received through a backward packet such that the real time data of
the previous frame can be re-transmitted or a channel change is
requested; a transmission/reception controller for performing
forward packetization for real time data outputted from the
transmission data generation unit together with header information
to transmit the forward packet through a setting channel, such that
a channel without channel interference is searched for per a
replacement channel test period to store the searched channel as a
replacement channel, and present setting channel can be changed to
the replacement channel when channel change of the memory
controller is requested; and an RF transmitting/receiving unit for
communicating the forward packet and backward packet with the slave
side in wireless interface fashion.
[0010] In accordance with another aspect of the present invention,
there is provided a short distance wireless data transmission
system, which includes a transmission data generation unit for
adding a redundancy to data to be transmitted and then outputting
the data, and a received data processing unit for recovering data
included in a wirelessly received backward packet to original data,
as an error bit is searched for using the redundancy included in
the wirelessly received backward packet, and then outputting the
original data, the system comprising: a memory controller for
storing real time data, which is recovered in the receiving data
processing unit, in a memory address which is indicated by record
position information within a forward packet, for generating
subsequent record position indication information indicating the
memory address in which real time data of the subsequent forward
packet must be stored, and output position indication information
of real time data which is presently outputted from a memory, and
for outputting the information thereto; a transmission/reception
controller for variably setting a setting channel according to
control information within wireless received forward packet, for
performing backward packetization for subsequent record position
indication information and output position indication information,
which is inputted from the memory controller, together with
non-real time data, and for transmitting the packet thereto; and an
RF transmitting/receiving unit for communicating the forward packet
and backward packet with the master side in a wireless interface
fashion.
[0011] According to the above-mentioned configuration, as the
master side designates position information in a memory, in which
transmitted real time data must be recorded, and the slave side
returns position information, which records real time data
subsequent to the transmitted real data, to the master side, the
master side compares the designated position information with the
returned position information to determine as to whether data loss
occurs due to channel interference, such that it can re-transmit
the data if data loss occurs.
[0012] Here, since the master side is buffering the real time data,
an amount of buffered data is monitored and the same data is
repeatedly transmitted. Namely, if the data amount of the buffered
memory exceeds a predetermined reference value, a setting channel
is changed to a new replacement channel without interference to
perform re-transmission from the first lost data. Therefore, the
short distance wireless data transmission system according to the
present invention can prevent data loss due to channel
interference.
DESCRIPTION OF DRAWINGS
[0013] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0014] FIG. 1 is a block diagram of a short distance wireless data
transmission system according to an embodiment of the present
invention;
[0015] FIG. 2 is a block diagram of a packet transmitted/received
from/by a short distance wireless data transmission system
according to an embodiment of the present invention;
[0016] FIG. 3 is a flow chart for describing a search procedure of
a replacement channel for performing short distance wireless data
transmission according to an embodiment of the present
invention;
[0017] FIG. 4 is a flow chart for describing a channel change
procedure according to an embodiment of the present invention, in a
case where successive interference occurs in setting channel;
[0018] FIG. 5 illustrates time axes showing the search procedure of
replacement channel illustrated in FIG. 3; and
[0019] FIG. 6 illustrates time axes showing the channel change
procedure illustrated in FIG. 4.
BEST MODE
[0020] Now, preferred embodiments of the present invention will be
described in detail with reference to the annexed drawings. In the
following description, a detailed description of known functions
and configurations incorporated herein will be omitted when it may
make the subject matter of the present invention rather
unclear.
[0021] FIG. 1 is a block diagram of a short distance wireless data
transmission system according to an embodiment of the present
invention. FIG. 2 is a block diagram of a packet
transmitted/received from/by a short distance wireless data
transmission system according to an embodiment of the present
invention.
[0022] Firstly, when a short distance wireless data transmission
system located at a master side according to an embodiment of the
present invention inputs real time data R/L SURROUND from a decoder
AC-3 which processes signals reproduced in optical media, the
system can packetized the data and performs short distance wireless
data transmission for the packets based on the configuration of
FIG. 1. Afterwards, a short distance wireless data transmission
system located at a slave side receives and processes the wireless
transmitted packets such that audio reproduced in the optical media
can be outputted through a speaker. With reference to the attached
drawings, the procedures are described in detail below.
[0023] The short distance wireless data transmission systems
according to an embodiment of the present invention includes a
memory controller 100, a memory 110, a transmitting data generation
unit 120, a receiving data processing unit 130, a
transmission/reception controller 140, and an RF
transmitting/receiving unit 150.
[0024] When the short distance wireless data transmission systems
is operated as a master, the memory controller 100 stores real time
data from a decoder in the memory 110, and reads real time data,
which is necessary for a packet, from the memory 100 to output the
data to the transmission data generation unit 120 which will be
described later. Also, the memory controller 100 at the master side
determines as to whether there is a retransmission request of real
time data transmitted to a previous frame through a backward packet
transmitted from the slave side, if the retransmission request
exists, variation amount of data stored in the memory 110 is
checked. After that, the memory controller 100 retransmits real
time data, which was transmitted to the previous frame, thereto, or
requests a channel change to the transmission/reception controller
140.
[0025] The channel change request procedure and the check procedure
for variation amount of data stored in the memory 100 will be
described in detail later, with reference to FIG. 3 and FIG. 4.
[0026] When the short distance wireless data transmission system is
operated as a slave, the memory controller 100 stores real time
data, which is recovered in the receiving data processing unit 130,
which will be described later, in an address of memory 100
indicated by record position information within a forward packet
transmitted from the master. Also, the system generates subsequent
record position indication information indicating an address of the
memory 100 in which real time data of a subsequent forward packet
must be stored, and output position indication information of real
time data currently outputted from the memory 110, and then outputs
them thereto. Such procedures will be described in detail later,
with reference to FIG. 3 and FIG. 4.
[0027] Each transmission data generation unit 120 at the master and
slave sides adds minimum redundancy for performing error recovery
to data (real time data and non-real time data) to be transmitted,
and then outputs them thereto. Such a transmission data generation
unit 120 includes a compression unit for compressing real time data
like the prior art short distance wireless data transmission
system, a scrambler for scrambling compressed real time data, an RS
encoder/interleaver, and a forward error correction (FEC)
encoder.
[0028] The receiving data processing unit 130 searches for error
bits to recover and output the original data, using the redundancy
included in received packets (forward packet, backward packet). In
order to recover the data processed in the transmission data
generation unit 120, such receiving data processing unit 130
includes a de-interleaver, an RS decoder, a de-scrambler, a
recovering unit and FEC decoder.
[0029] On the other hand, the transmission/reception controller 140
at the master side performs forward packetization for real time
data and non-real time data, which are inputted from the
transmission data generation unit 120, together with header
information, and then transmits the forward packets through a
setting channel. Also, the transmission/reception controller 140
searches for channels which do not have channel interference, and
then stores the searched channels therein as a replacement channel.
Afterward, when the memory controller 100 requests a channel change
request, the transmission/reception controller 140 changes the
currently set channel (hereinafter referred to as a `setting
channel`) to the replacement channel, thereby communicating with
the slave. Program data for such a procedure are stored in an
internal memory included in the transmission/reception controller
140.
[0030] On the contrary, the transmission/reception controller 140
at the slave side variably sets a current setting channel to a
replacement test channel or a replacement channel. Also, the
transmission/reception controller 140 performs backward
packetization for subsequent record position indication information
inputted from the memory controller 100 at the slave side together
with non-real time data, and then transmits the packets
thereto.
[0031] Here, the transmission/reception controller 140 has a
function to detect sync information. Also, although the memory
controller 100 and the transmission/reception controller 140 are
illustrated in FIG. 1 with separation, they can be implemented with
a single IC chip. In addition, the single IC chip may further
include the transmitting data generation unit 120 and the receiving
data processing unit 130.
[0032] The RF transmitting/receiving units 150, which are included
in the respective short distance wireless data transmission system
at the master and slave sides, communicate packets with one
another, in a wireless interface fashion.
[0033] With reference to FIG. 2, packets transmitted/received
between the short distance wireless data transmission system at the
master and slave sides are described in detail.
[0034] Firstly, a forward packet transmitted from a master to a
slave includes a sync field in which sync information is recorded,
a control information field in which communication channel
indication information is recorded, a header field in which record
position information for indicating record position of real time
data and output position information for indicating output position
of data in a memory, and a field in which real time data and
non-real time data are recorded, respectively.
[0035] On the other hand, a backward packet transmitted from a
slave to a master includes a sync field in which sync information
is recorded, a control information field in which a response
message (RM) is recorded, a header field in which subsequent record
position indication information indicating an address of the memory
in which real time data must be stored, and an output position
indication information of real time data currently outputted from
the memory, and a field in which non-real time data are
recorded.
[0036] Here, the record position information and output position
information, which are included in the forward packet, are
generated in the memory controller 100 at the master side, and
provided to the transmission/reception controller 140. Also, the
subsequent record position indication information and the output
position indication information, which are included in the backward
packet, are generated in the memory controller 100 at the slave
side, and provided to the transmission/reception controller 140 at
the slave side.
[0037] Although the above-mentioned description about each block
for processing real time data and non-real time data is based on
figures, circuit configuration can be modified to comply with uses
of the master and slave. Namely, when the system is used as a
slave, the transmission data generating unit 120 can be modified as
function blocks for generating real time data or must be removed
therefrom.
[0038] A method for transmitting data in the above-mentioned short
distance wireless data transmission system is described in detail
below.
[0039] Each transmission/reception controller 140, which is
included in the short distance wireless data transmission systems
at the master and slave sides, set a channel frequency for data
packet transmission after a system initialization procedure. Here,
such a channel set for data packet transmission is referred to as a
"setting channel."
[0040] The embodiment according to the present invention selects 10
of 79 frequencies of a 2.4 GHz band, which are evenly spread, in
order to perform a connection trial. Namely, the embodiment selects
frequencies (0, 8, 16, . . . , 72) corresponding to a multiple of
8. Here, such selection is performed because the system is randomly
operated with respect to these frequencies at the initial time and
time for searching for a frequency through which
transmission/reception are successive can be saved. When
transmission/reception are successive through one of the
above-mentioned frequency channels, the transmission/reception
controller 140 at the master side determines that there is no
interference for a channel in the vicinity of the channel through
which transmission/reception are successive, and then selects the
vicinity channel as a first setting channel Fc.
[0041] When a setting channel is selected on the basis of the
above-mentioned procedure, the master and slave performs
transmission/reception of real time data therebetween through the
setting channel Fc. Namely, the real time data outputted from the
decoder starts to be recorded in the memory 110 through the memory
controller 100 at the master side. The embodiment according to the
present invention is implemented under the assumption that size of
real time data recorded in the memory 10 is 120 bytes and size of
real data outputted from the memory 110 is 144 bytes.
[0042] If real data necessary for packetization is recorded in the
memory 110, the memory controller 110 reads real time data for
forward packetization of 144 bytes from the memory 110, and then
outputs them to transmission data generation unit 120. Also, the
memory controller 110 outputs record position information for
indicating record position of real time data (, which corresponds
to address information recorded in the memory 110) to the
transmission/reception controller 140. After that, the
transmission/reception controller 140 at the master side performs
forward packetization for the header information, which includes
the record position information, real time data and control
information, and then outputs the forward packet to the RF
transmitting/receiving unit 150 in a wireless fashion.
[0043] Such forward packets are transmitted through a setting
channel in a data transmission interval, and through a replacement
channel in a channel test interval. As shown in FIG. 5, the
embodiment according to the present invention is implemented such
that 8 frames are configured as a super frame, data transmission is
performed in 7 frames in the super frame through the setting
channel Fc, and a channel test is performed in one channel.
[0044] With respect to FIG. 3 to FIG. 5, a procedure from testing
for a temporary replacement channel to storage of the tested
channel as a substantial replacement channel is described
below.
[0045] Firstly, the transmission/reception controllers 140 at the
master and slave sides sets a channel frequency for mutual
communication therebetween in step 200, in which the channel
frequency is a setting channel Fc.
[0046] When the setting channel Fc without interference is found,
the transmission/reception controller 140 at the master side forms
a forward packet having a structure shown in FIG. 2, and then
transmits real time data, in which control information in the
transmitted forward packet includes an AM message, in step 210. The
AM message is a command indicating that a backward packet is
transmitted through a present setting channel Fc. When the
transmission/reception controller 140 at the slave side receives
the forward packet including such an AM message, it correspondingly
transmits a backward packet whose control information includes a
response message RM to the master side in step 220.
[0047] The transmission/reception controller 140 at the master side
accumulates error bit of sync field in the backward packet received
through the setting channel Fc in step 230. Such accumulation is a
method to check as to whether channel interference exists. As
demand occasions, the method may check as to a number of error bits
in real time data or non-real time data, which are inserted in the
received packet.
[0048] Afterwards, the transmission/reception controller 140 at the
master side, which accumulates error bit of sync field in the
backward packet, checks as to whether a replacement channel test
period is identified, in step 240. As shown in FIG. 5, the
embodiment according to the present invention is implemented such
that, the replacement channel test period is identified in the
super frame period, or 8th frame. If the replacement channel test
period is not identified on the basis of the test result of step
240, the transmission/reception controller 140 at the master side
retransmits the forward packet including the AM message to the
slave side through the present channel, or the setting channel Fc,
and receives a backward packet including an RM message
corresponding to the transmitted forward packet to accumulate error
bit of sync field. The embodiment according to the present
invention is implemented such that the transmission/reception
controller 140 at the master side accumulates error bit of sync
field for backward packets of 7 frames.
[0049] On other hand, if the replacement channel test period is
identified on the basis of the test result of step 240, the
transmission/reception controller 140 at the master side transmits
a forward packet including an AMTx message, indicative of change
toward a replacement channel for testing, to the slave side in step
250, and then changes the setting channel of the
transmission/reception controller 140 to a replacement channel for
testing. The AMTx message includes replacement channel information
for testing. Here, the replacement channel for testing, which is
temporarily set in the replacement channel test interval, is
preferably set to a frequency channel which is spaced apart from
the present setting channel Fc by a predetermined distance, in
order to prevent channel interference. Because there is high
probability of channel interference at frequencies in a vicinity of
setting channel Fc in which channel interference is generated. The
replacement channel for testing is denoted by F1 in FIG. 5.
[0050] On the other hand, when control information in the received
forward packet includes the AMTx message requesting change of the
setting channel in step 260, the transmission/reception controller
140 at the slave side changes the present setting channel Fc to a
replacement channel for testing, which is indicated by the forward
packet, in step 270. Afterwards, the transmission/reception
controller 140 at the slave side transmits a backward packet
including an RM message through a corresponding replacement channel
for testing in step 280.
[0051] Accordingly, the transmission/reception controller 140 at
the master side receives the backward packet through the
replacement channel for testing, and calculates error bit of sync
field in the received backward packet in step 300. Afterwards,
based on the calculation, the transmission/reception controller 140
determine as to whether the present replacement channel for testing
can be set as a proper replacement channel in step 310. Such
determination method is performed such that the error bit of sync
field in the replacement channel test interval within the super
frame is compared with accumulation average of error bit of sync
field in the data transmission interval within a corresponding
super frame.
[0052] If the error bit of sync field of the backward packet, which
is received through the replacement channel for test F1, is less
than the accumulation average of error bit of sync field of the
backward packet, which is received through the setting channel Fc
in the data transmission interval within the same super frame, the
replacement channel for test F1 is determined to have very small
channel interference.
[0053] Consequently, the transmission/reception controller 140 at
the master side firstly sets a replacement channel for testing in a
replacement channel test interval within a super frame, which is
periodically performed, and then stores the replacement channel for
testing therein as a replacement channel, if the error bit of sync
field of the backward packet, which is received through the channel
is less than the accumulation average of error bit of sync field of
the backward packet, which is received the data transmission
interval within a corresponding super frame. Also, the
transmission/reception controller 140 successively checks as to
whether channel interference is generated in the stored replacement
channel at every replacement channel test interval within the
repeated super frame, through step 210 to step 310. If successive
interference is generated in the replacement channel, a new
replacement channel for test F2 is set in step 320 to check channel
interference. If the check result shows no channel interference,
the replacement channel for test F2 is set to a new replacement
channel.
[0054] With reference to FIG. 4 and FIG. 6, described is a
procedure where teal time data transmitted through the setting
channel Fc are newly transmitted through the replacement channel
(F1 or F2) due to successive interference.
[0055] Firstly, real time data, which is processed by forward
packetization and transmitted through the setting channel Fc, is
recovered through the received data processing unit 130 at the
slave side, and then stored in the memory 110 according to control
of the memory controller 100 at the slave side. Here, the real data
is stored at an address of the memory, which is indicated by record
position information (for example, A0) included in the received
forward packet. When the real time data is completely stored in the
memory address indicated by the record position information (A0),
the memory controller 100 at the slave side generates subsequent
record position indication information (for example, A1) indicating
an memory address in which real time data of subsequent forward
packet, and then outputs the memory address to the
transmission/reception controller 140 at the slave side. The
subsequent record position indication information A1 is included in
the backward packet to be inputted to the memory controller 100 at
the master side. Here, the memory controller 100 at the slave side
controls the memory 110 such that stored real time data can be
outputted only if the real time data are stored in the memory 110
exceeds the predetermined critical value. Also, the memory
controller 100 at the slave generates output position indication
information An of the real time data presently outputted from the
memory 110 and then transmits the information to the
transmission/reception controller 140 at the slave side. According
to the output position indication information An, real time data of
the slaves, which are connected to the master at different time
points, can be synchronously outputted thereon. Namely, when the
real time data are stored in the memory address indicated by output
position information within the forward packet, the memory
controller 100 at the slave side reads the real time data in the
memory and then performs output control.
[0056] Such a memory controller 100 at the slave side generates
subsequent record position indication information and output
position indication information to be inputted to the
transmission/reception controller 140 at the at the slave side. The
transmission/reception controller 140 at the salve performs
backward packetization for the inputted information and non-real
time data, and then transmits them to the master.
[0057] The master side inputs the backward packet including the
subsequent record position indication information and output
position indication information, in which the received information
is recovered in the received data processing unit 130 and then
inputted to the memory controller 100 at the master side.
[0058] The memory controller 100 at the master side checks as to
whether there is a re-transmission request of real time data, which
are transmitted in a previous frame, from the recovered information
in step 400. Such a check method is performed such that the record
position information of the real time data, which is transmitted in
a previous frame, is compared with subsequent record position
indication information within the backward packet. For example,
when the record position information of the real time data, which
is transmitted in a previous frame, is A0, if subsequent record
position indication information, which is received through the
backward packet, is A0, such a result means that the real time data
is not normally transmitted thereto due to channel
interference.
[0059] As such, based on determination as to whether there is a
data re-transmission request, if there is a data re-transmission
request, the memory controller 100 at the master side checks as to
whether such a retransmission request successively exists in step
410. If the check result show no successive interference situation,
the memory controller 100 stores an amount of data, which is
presently stored in the memory 110, or a memory amount, in step
420, and then re-transmits real time data, which is transmitted in
a previous frame, thereto through the setting channel Fc.
[0060] On the other hand, if the check result is a successive
interference situation, the memory controller 100 at the master
side proceeds to step 430 and then calculates variation amount of
data stored in the memory. Here, the variation amount of data is
memory amount stored in step 420, which is calculated as present
memory amount is subtracted from memory amount when the first
re-transmission is requested. If the variation amount of memory
data in the real time data re-transmission interval exceeds a
channel variation reference value in step 440, the memory
controller 100 at the master side determines that there is a
successive interference in the setting channel Fc, and then
requests a change toward the replacement channel to the
transmission/reception controller 140 at the master side in step
450, in which the replacement channel is tested in FIG. 3 to
prevent loss of real time data.
[0061] Namely, the memory controller 100 at the master side checks
as to whether memory data variation satisfies a channel change
condition from a time when the first re-transmission is requested
to the present time, when data re-transmissions are repeatedly
requested. When the determination is positive, re-transmission is
no longer performed and instead a change toward the replacement
channel having been tested is requested.
[0062] When a change toward the replacement channel is requested,
the transmission/reception controller 140 at the master side
transmits a forward packet, in which an AMCx message indicative of
a channel change is included as control information, to the slave
side, such that the master and slave can change present setting
channel Fc to the replacement channel F1 without interference.
[0063] Afterwards, the master side re-reads real time data, which
must be previously and repeatedly re-transmitted, from the memory,
and then performs re-transmission, such that the slave side can
receive the repeatedly re-transmitted real time data and a series
of real time data which are subsequent therefrom.
[0064] Therefore, although a change towards a replacement channel
is performed due to successive channel interference, the system
according to the present invention cannot lose real time data.
[0065] FIG. 6(a) and FIG. 6(b) illustrate examples each of which
shows that a setting channel Fc is changed to a replacement channel
F1, in which such a change is performed because successive channel
interference is existed in the setting channel Fc. Here, notations
D and E denote frequency channel change times of the slave,
respectively.
[0066] The short distance wireless data transmission system
according to the present invention can monitor variation amount of
memory data, which is buffered in the master side when data
transmission errors occur, can perform re-transmission of data
having transmission errors, and can perform a change toward new
replacement channel without interference if variation amount of
memory data, which is buffered therein, exceeds a predetermined
reference value to re-transmit from data in which the first
transmission error occurs thereto, such that real time data cannot
be lost, although a channel change is generated by successive
channel interference.
[0067] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *